Issue Filling Hole in Mesh
When you have a hole like this, don't press F to fill, otherwise you'll have one unique face and then you'll need to use J (join) or K (knife) to recreate 4 different faces and they won't even be correct, you 'll need to pull the central vertex to get the right curve:

What you should do instead is selecting 3 vertices on each side:

Then CtrlF (Face) &gt; Grid Fill to fill, and tweak the parameters in the Operator box (bottom left of your 3D view) if necessary: